1. Field of the Invention
The present invention relates to an engine air intake system, particularly a resin air intake system provided with an intake control valve, designed to make the air intake system be provided with an air intake control valve of a resin.
2. Description of Related Art
Requirements for higher performance engines in recent years have resulted in using a variety of systems for air intake systems. There is known a so-called variable air intake system to improve both the engine torque in the medium to low speed range and to improve output in the high speed region. These try to increase the engine fueling efficiency by varying the essential air intake type lengths or capacity of the air intake system according to the engine operating conditions, so as to make effective use of inertial and resonance actions under a given situation.
In order to change the air intake tube length or capacity, such a variable air intake system equips the air intake constituting part, such as an air intake manifold, with air intake passages open to be connected to each combustion chamber of an engine with intake control valves rotatably, which are supported by a shaft having an axis in the direction perpendicular to the axes of the openings. Driving this shaft with an external actuator is designed to control the opening and closing of the intake control valve.
There is known a lean combustion engine for improved engine fuel consumption rate for energy saving, in which its air intake manifold is provided with a plurality of air intake passages per cylinder, and controlling the opening and closing of an intake control valve provided for one of the air intake passages is designed to give an air intake with a swirl within the designated operating range.
In general, such an air intake manifold is cast from a metal such as aluminum and bearing holes to support the above shaft rotatably are drilled by machining after casting. A split butterfly valve for a manifold is disclosed in FR-A-2606115. Two halves of the manifold can be molded from a metal or an appropriate plastic. The butterfly is positioned on a shaft and secured in the split housing. The securing and positioning means are complicated in that recesses are cut into positioning flanges on both halves.